Soldiers around the world have something very basic in common. They need to eat.

Perhaps unsurprisingly, field rations have a pretty bad reputation. They are known among U.S. soldiers as "Meals, Ready to Eat," or "MREs." The MREs are freeze-dried and vacuum-sealed.

The troops have to rely on these meals while out on patrol or on the battlefield. No one expects field rations to provide a great dining experience. But many militaries do what they can to give their soldiers a decent meal. This might be done by serving a country's traditional fare. But some are measuring how eating MREs can affect their troops' health.

For American soldiers, Army-issued MREs come packed with everything soldiers need for a solid 1,200-calorie meal. The MREs include several courses. In addition, MREs include beverages. They also include flameless heating elements and utensils. But the Army isn't only concerned about fueling its soldiers. It wants them to enjoy their meal.

"What is nutrition if you don't consume the food?" says Holly McClung. She is an Army research dietitian. "We need ways to keep warfighters interested in and excited about eating in the field." After all, they have been training and eating MREs for several days.

The U.S. Army put out a call for volunteers. The Army wanted to find out who was willing to survive solely off of MREs. The volunteers would eat MREs only. And they would eat them for almost a month. The goal was to see how the field rations might affect the delicate ecosystem of gut bacteria in the digestive system.

MREs have to meet a laundry list of requirements. The requirements include being able to survive a 1,250-foot parachute drop. The MREs must also stay edible for up to 3 1/2 years in temperatures of up to 80 degrees. It should be no surprise that officers would want to know how these changes might affect their troops health. This is according to reporter Emanuella Grinberg. She works for CNN.

"Interactions between the millions of bacteria living in our gut and what we eat is a very important factor in gut health. But we don't know how MRE foods interact with those bacteria to impact gut health," McClung said in a statement.

"Ultimately, discovering how eating MREs influences gut bacteria and gut health will help our efforts to continually improve the MRE."

Studying how eating MREs affect soldiers' microbiomes is one way that U.S. Army officials are trying to keep their troops healthy. The Army also does what it can to make sure that soldiers aren't eating the same meals over and over.

MREs cover a wide range of food. They include spaghetti Bolognese and caffeine-infused beef jerky, David Whelan reports for Munchies. Army researchers even unveiled something new. It is what some call the ''holy grail of MRE's.'' You might call it pizza.

Most countries try to offer their soldiers something that is like their homeland's cuisine. South Korean soldiers get treated to bibimbap and kimchi. French fighters are offered deer pâté and duck confit. The range of food varies greatly. Colombian soldiers mostly live off of rice and beans. The Italian Army issues its fighters a 40-percent alcohol "breakfast shot," Whelan writes.

"When you're in the deployed environment, it tends to be fear and the monotonous. So the only thing you have to look forward to is the chow," Army Materiel Command director Bill Bigelow tells C.J. Lin for Stars and Stripes. "And if it's monotonous chow, that just adds to your misery."